This invention relates to temperature indicators and more particularly to apparatus of the type wherein the heating of an indicator to a predetermined temperature produces a change in color of a visual indicator.
While the invention of this application has broad uses in those areas where it is desired to give an indication as to when a temperature limit has been reached, the preferred embodiment is directed more particularly to temperature indicating fasteners.
One application of a temperature indicating fastener that has received some attention in the prior art is that with respect to railroad axle bearings.
A typical manner of mounting a railroad car body is to support such body on a pair of truck units. Generally, each truck unit includes a pair of longitudinally spaced axles having exteriorly projecting journal portions. Each axle is rotatably mounted to the truck by means of a pair of bearing assemblies.
A typical bearing assembly will be pressed on the railroad car axle as a completely sealed and prelubricated unit. This assembly will include a bearing, an axle end cap, a plurality of cap screws and a locking plate. The cap screws are adapted to be received in tapped holes provided in the axle.
For obvious reasons it is desirable to be able to detect an overheating condition in a railroad axle bearing. The presence of excessive heat not only causes lubricant to be dissipated but, in extreme conditions, may also result in a seizing of the bearing.
Accordingly, it has been known in the prior art to provide some means for indicating temperature in one or more of the bolts used in association with the bearing assembly in a railroad car axle. It follows that as heat is generated by a bearing it will be transmitted to the axle and subsequently to the fastener of the bearing assembly since such fastener is directly received in the axle.
One example of a prior art effect toward providing a temperature indicator in a railroad bearing bolt is shown in U.S. Pat. No. 3,442,249 to Jamison et al. In the Jamison structure a fusible material is provided in the bolt head such that when the bolt overheats the material will be caused to melt and flow outwardly thereby permitting detection of overheating of the roller bearing unit of the axle merely by visual inspection.
Another structure of the prior art is described in U.S. Pat. No. 3,877,411 to MacDonald. MacDonald teaches the application of a heat sensitive chemical wafer or disc to a recessed portion of the head of a bolt. When the bolt is heated to a temperature that exceeds the predetermined temperature limit for the bolt, the disc of the bolt head will change color thereby giving a visual indication of the fact that a specific temperature limit has been reached.
Other signalling devices have been used in the prior art in connection with railroad axle bearings including devices designed to emit smoke or noxious odors at such time as the bearing has reached a predetermined critical temperature.
This invention is directed to a temperature indicator for particular use and adaptation in bearing bolts and wherein there is provided a means for sensing a temperature limit having been reached that does not rely on either a heat sensitive chemical or other materials of the type described above.